methane

(CH4)

(compound of one carbon and 4 hydrogen atoms)

Methane (CH4) is a
compound with molecules each consisting of one
carbon and four hydrogens atoms.
It is produced by biological processes on Earth, and is generally unstable,
thus constitutes a biosignature.
It can also be generated abiotically, but its observed presence
suggests some long-lasting process is generating it.
It is observed on some solar systemmoons.

If the molecule contains a deuterium atom,
which can be called CH3D, then
methods of tracing isotopes (e.g., varying spectra,
or varying mass) can be used to characterize observed
chemical reactions. This has been done
using spectrograms of Titan's atmosphere
taken by Keck Observatory.